Silver composition for micro-deposition direct writing silver conductor lines on photovoltaic wafers

ABSTRACT

Embodiments of the invention relate to a silicon semiconductor device, and a conductive thick film composition for use in a solar cell device.

FIELD OF THE INVENTION

Embodiments of the invention relate to a silicon semiconductor device,and a conductive thick film composition for use in a solar cell device.

TECHNICAL BACKGROUND OF THE INVENTION

A conventional solar cell structure with a p-type base has a negativeelectrode that may be on the front-side (also termed sun-side orilluminated side) of the cell and a positive electrode that may be onthe opposite side. Radiation of an appropriate wavelength falling on ap-n junction of a semiconductor body serves as a source of externalenergy to generate hole-electron pairs in that body. Because of thepotential difference which exists at a p-n junction, holes and electronsmove across the junction in opposite directions and thereby give rise toflow of an electric current that is capable of delivering power to anexternal circuit. Most solar cells are in the form of a silicon waferthat has been metalized, i.e., provided with metal contacts that areelectrically conductive.

There is a need for compositions, structures (for example,semiconductor, solar cell or photodiode structures), and semiconductordevices (for example, semiconductor, solar cell or photodiode devices)which have improved electrical performance, and methods of making.

SUMMARY OF THE INVENTION

An embodiment of the invention relates to composition including: (a) oneor more conductive materials; (b) one or more inorganic binders; and (c)organic vehicle, wherein 1 to 15% of the inorganic components aresubmicron particles. In an embodiment, 85 to 99% of the inorganiccomponents may have a d50 of 1.5 to 10 microns. In an embodiment, one ormore conductive materials may include silver. In an embodiment, aportion of the silver contains submicron particles. In an embodiment,the submicron particles have a d50 of 0.1 to 1 microns. In anembodiment, the submicron particles have a d50 of 0.1 to 0.6 microns. Inan embodiment, the particles have a bimodal size distribution.

The composition may include one or more additives selected from thegroup consisting of: (a) a metal wherein said metal is selected from Zn,Pb, Bi, Gd, Ce, Zr, Ti, Mn, Sn, Ru, Co, Fe, Cu, and Cr; (b) a metaloxide of one or more of the metals selected from Zn, Pb, Bi, Gd, Ce, Zr,Ti, Mn, Sn, Ru, Co, Fe, Cu and Cr; (c) any compounds that can generatethe metal oxides of (b) upon firing; and (d) mixtures thereof. In anembodiment, the additives may include ZnO, or a compound that forms ZnOupon firing. In an embodiment, the ZnO and/or inorganic binder mayinclude submicron particles. The ZnO may be 2 to 10 wt % of the totalcomposition. The glass frit may be 1 to 6 wt % of the total composition.The conductive material may include Ag. The Ag may be 90 to 99 wt % ofthe solids in the composition. In an embodiment, the inorganiccomponents may be 70 to 95 wt % of the total composition.

A further embodiment relates to a method of manufacturing asemiconductor device including the steps of: (a) providing asemiconductor substrate, one or more insulating films, and the thickfilm composition described herein; (b) applying the insulating film tothe semiconductor substrate; (c) applying the thick film composition tothe insulating film on the semiconductor substrate, and (d) firing thesemiconductor, insulating film and thick film composition. In an aspect,the insulating film may include one or more components selected from:titanium oxide, silicon nitride, SiNx:H, silicon oxide, and siliconoxide/titanium oxide.

A further embodiment relates to a semiconductor device made by themethods described herein. An aspect relates to a semiconductor deviceincluding an electrode, wherein the electrode, prior to firing, includesthe composition described herein. An embodiment relates to a solar cellincluding the semiconductor device.

An embodiment relates to a semiconductor device including asemiconductor substrate, an insulating film, and a front-side electrode,wherein the front-side electrode comprises one or more componentsselected from the group consisting of zinc-silicate, willemite, andbismuth silicates.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a process flow diagram illustrating the fabrication of asemiconductor device.

Reference numerals shown in FIG. 1 are explained below.

-   -   10: p-type silicon substrate    -   20: n-type diffusion layer    -   30: silicon nitride film, titanium oxide film, or silicon oxide        film    -   40: p+ layer (back surface field, BSF)    -   60: aluminum paste formed on backside    -   61. aluminum back electrode (obtained by firing back side        aluminum paste)    -   70: silver or silver/aluminum paste formed on backside    -   71: silver or silver/aluminum back electrode (obtained by firing        back side silver paste)    -   500: silver paste formed on front side according to the        invention    -   501: silver front electrode according to the invention (formed        by firing front side silver paste)

DETAILED DESCRIPTION OF THE INVENTION

There is a need for improved solar cells with increased efficiency.There is a need for conductive compositions suitable for the formationof narrow conductor lines with increased height. An aspect of theinvention relates to compositions containing submicron particles. Thecompositions may be thick film compositions. These compositions may beused to form solar cell electrodes. The electrodes may be on thefront-side of a solar cell. In an embodiment, the electrode lines may benarrow and have increased height.

As used herein, “thick film composition” refers to a composition which,upon firing on a substrate, has a thickness of 1 to 100 microns. Thethick film compositions may contain a conductive material, a glasscomposition, and organic vehicle. The thick film composition may includeadditional components. As used herein, the additional components aretermed “additives”.

The compositions described herein include one or more electricallyfunctional materials and one or more glass frits dispersed in an organicmedium. These compositions may be thick film compositions. Thecompositions may also include one or more additive(s). Exemplaryadditives may include metals, metal oxides or any compounds that cangenerate these metal oxides during firing.

In an embodiment, the electrically functional powders may be conductivepowders. In an embodiment, the composition(s), for example conductivecompositions, may be used in a semiconductor device. In an aspect ofthis embodiment, the semiconductor device may be a solar cell or aphotodiode. In a further aspect of this embodiment, the semiconductordevice may be one of a broad range of semiconductor devices. In anembodiment, the semiconductor device may be a solar cell.

In an embodiment, the thick film compositions described herein may beused in a solar cell. In an aspect of this embodiment, the solar cellefficiency may be greater than 70% of the reference solar cell. In afurther embodiment, the solar cell efficiency may be greater than 80% ofthe reference solar cell. The solar cell efficiency may be greater than90% of the reference solar cell.

In an embodiment, the ratio of organic medium in the thick filmcomposition to the inorganic components in the dispersion may bedependent on the method of applying the paste and the kind of organicmedium used, as determined by one of skill in the art. In an embodiment,the dispersion may include 70-95 wt % of inorganic components and 5-30wt % of organic medium (vehicle) in order to obtain good wetting.

In an embodiment, a portion of the inorganic components may be submicronparticles. In an aspect of this embodiment, the submicron particles mayhave a d50 of 0.1 to 1 microns. In a further aspect, the submicronparticles may have a d50 of 0.1 to 0.8 microns. In a further aspect, thesubmicron particles may have a d50 of 0.2 to 0.6 microns.

In an embodiment, the submicron particles may be 1 to 15 wt % of thecomposition. In a further embodiment, the submicron particles may be 2to 10 wt % of the composition. In a further embodiment, the submicronparticles may be 3 to 6 wt % of the composition.

In an embodiment, the submicron particles may include a portion of theconductive material. In an aspect, 1 to 15 wt % of the conductivematerial may be submicron particles. In a further aspect, 2 to 10 wt %of the conductive material may be submicron particles. In a furtheraspect, 3 to 6 wt % of the conductive composition may be submicronparticles.

In an embodiment, a portion of the composition may have a d50 of 1.5 to10 microns. In an aspect of this embodiment, 85 to 99 wt % of theinorganic components of the composition may have a d50 of 1.5 to 10microns. In an aspect of this embodiment, a portion of the compositionmay have a d50 of 2.0 to 7.0 microns. In an aspect of this embodiment, aportion of the composition may have a d50 of 2.5 to 5.0 microns.

In a further aspect, the conductive material may include silver. In anaspect, 50 to 100 wt % of the conductive material may be silver. In afurther aspect, 70 to 99 wt %, 70 to 98 wt %, or 80 to 95 wt % of theconductive material may be silver.

Glass Frits

In an aspect of the invention, the composition includes glass fritcompositions. Glass frit compositions useful in the present inventionwill readily recognized by one of skill in the art. Glass fritcompositions useful in compositions used to make front-side solar cellelectrodes may be used, for example. Exemplary glass frit compositionsinclude lead borosilicate glasses. In an embodiment, glass fritscompositions useful in the present invention may include 20-24 wt %SiO₂, 0.2-0.8 wt % Al₂O₃, 40-60 wt % PbO, and 5-8 wt % B₂O₃. In anembodiment, the glass frit composition may optionally also include 3-7wt % TiO₂. In an embodiment, the glass frit composition may optionallyalso include one or more fluorine-containing components, including butnot limited to: salts of fluorine, fluorides, metal oxyfluoridecompounds, and the like. Such fluorine-containing components include,but are not limited to PbF₂, BiF₃, AlF₃, NaF, LiF, KF, CsF, ZrF₄, TiF₄and/or ZnF₂. In an embodiment, the glass frit composition may include8-13 wt % PbF₂.

In a further aspect of this embodiment, thick film composition mayinclude electrically functional powders and glass-ceramic fritsdispersed in an organic medium. In an embodiment, these thick filmconductor composition(s) may be used in a semiconductor device. In anaspect of this embodiment, the semiconductor device may be a solar cellor a photodiode.

Conductive Materials

In an embodiment, the thick film composition may include a functionalphase that imparts appropriate electrically functional properties to thecomposition. In an embodiment, the electrically functional powder may bea conductive powder. In an embodiment the electrically functional phasemay include conductive materials (also termed conductive particles,herein). The conductive particles may include conductive powders,conductive flakes, or a mixture thereof, for example.

In an embodiment, the conductive particles may include Ag. In a furtherembodiment, the conductive particles may include silver (Ag) andaluminum (Al). In a further embodiment, the conductive particles may,for example, include one or more of the following: Cu, Au, Ag, Pd, Pt,Al, Ag—Pd, Pt—Au, etc. In an embodiment, the conductive particles mayinclude one or more of the following: (1) Al, Cu, Au, Ag, Pd and Pt; (2)alloy of Al, Cu, Au, Ag, Pd and Pt; and (3) mixtures thereof.

In an embodiment, the functional phase of the composition may includecoated or uncoated silver particles which are electrically conductive.In an embodiment in which silver particles are coated, they are at leastpartially coated with a surfactant. In an embodiment, the surfactant mayinclude one or more of the following non-limiting surfactants: stearicacid, palmitic acid, a salt of stearate, a salt of palmitate, lauricacid, palmitic acid, oleic acid, stearic acid, capric acid, myristicacid and linoleic acid, and mixtures thereof. The counter ion may be,but is not limited to, hydrogen, ammonium, sodium, potassium andmixtures thereof.

In an embodiment, the silver may be 60 to 90 wt % of the pastecomposition. In a further embodiment, the silver may be 70 to 85 wt % ofthe paste composition. In a further embodiment, the silver may be 75 to85 wt % of the paste composition. In a further embodiment, the silvermay be 78 to 82 wt % of the paste composition.

In an embodiment, the silver may be 90 to 99 wt % of the solids in thecomposition (i.e., excluding the organic vehicle). In a furtherembodiment, the silver may be 92 to 97 wt % of the solids in thecomposition. In a further embodiment, the silver may be 93 to 95 wt % ofthe solids in the composition.

As used herein, “particle size” is intended to mean “average particlesize”; “average particle size” means the 50% volume distribution size.Volume distribution size may be determined by a number of methodsunderstood by one of skill in the art, including but not limited toLASER diffraction and dispersion method using a Microtrac particle sizeanalyzer.

In an embodiment, a portion of the conductive materials may be submicronparticles. In an aspect of this embodiment, the submicron particles mayhave a d50 of 0.1 to 1 microns. In a further aspect, the submicronparticles may have a d50 of 0.1 to 0.8 microns. In a further aspect, thesubmicron particles may have a d50 of 0.2 to 0.6 microns.

In an embodiment, 1 to 15 wt % of the conductive material may besubmicron particles. In a further aspect, 2 to 10 wt % of the conductivematerial may be submicron particles. In a further aspect, 3 to 6 wt % ofthe conductive composition may be submicron particles.

In an embodiment, a portion of the conductive materials may have a d50of 1.5 to 10 microns. In an aspect of this embodiment, 85 to 99 wt % ofthe conductive materials may have a d50 of 1.5 to 10 microns. In anaspect of this embodiment, a portion of the conductive materials mayhave a d50 of 2.0 to 7.0 microns. In an aspect of this embodiment, aportion of the conductive materials may have a d50 of 2.5 to 5.0microns.

Additives

In an embodiment, the thick film composition may include one or moreadditives. In an embodiment, the additive may be selected from one ormore of the following: (a) a metal wherein said metal is selected fromZn, Pb, Bi, Gd, Ce, Zr, Ti, Mn, Sn, Ru, Co, Fe, Cu, and Cr; (b) a metaloxide of one or more of the metals selected from Zn, Pb, Bi, Gd, Ce, Zr,Ti, Mn, Sn, Ru, Co, Fe, Cu and Cr; (c) any compounds that can generatethe metal oxides of (b) upon firing; and (d) mixtures thereof.

In an embodiment, the additive may include a Zn-containing additive. TheZn-containing additive may include one or more of the following: (a) Zn,(b) metal oxides of Zn, (c) any compounds that can generate metal oxidesof Zn upon firing, and (d) mixtures thereof. In an embodiment, theZn-containing additive may include Zn resinate.

In an embodiment, the Zn-containing additive may include ZnO. In anembodiment, a portion of the ZnO may include submicron particles.

In an embodiment, ZnO may be present in the composition in the range of2-10 wt % total composition. In an embodiment, the ZnO may be present inthe range of 3-7 wt % total composition. In a further embodiment, theZnO may be present in the range of 4-6 wt % total composition.

Organic Medium

In an embodiment, the thick film compositions described herein mayinclude organic medium. The inorganic components may be mixed with anorganic medium, for example, by mechanical mixing to form pastes. A widevariety of inert viscous materials can be used as organic medium. In anembodiment, the organic medium may be one in which the inorganiccomponents are dispersible with an adequate degree of stability. In anembodiment, the rheological properties of the medium may lend certainapplication properties to the composition, including: stable dispersionof solids, appropriate viscosity and thixotropy for screen printing,appropriate wettability of the substrate and the paste solids, a gooddrying rate, and good firing properties. In an embodiment, the organicvehicle used in the thick film composition may be a nonaqueous inertliquid. The use of various organic vehicles, which may or may notcontain thickeners, stabilizers and/or other common additives, iscontemplated. The organic medium may be a solution of polymer(s) insolvent(s). In an embodiment, the organic medium may also include one ormore components, such as surfactants. In an embodiment, the polymer maybe ethyl cellulose. Other exemplary polymers include ethylhydroxyethylcellulose, wood rosin, mixtures of ethyl cellulose and phenolic resins,polymethacrylates of lower alcohols, and monobutyl ether of ethyleneglycol monoacetate, or mixtures thereof. In an embodiment. the solventsuseful in thick film compositions described herein include esteralcohols and terpenes such as alpha- or beta-terpineol or mixturesthereof with other solvents such as kerosene, dibutylphthalate, butylcarbitol, butyl carbitol acetate, hexylene glycol and high boilingalcohols and alcohol esters. In a further embodiment, the organic mediummay include volatile liquids for promoting rapid hardening afterapplication on the substrate.

In an embodiment, the polymer may be present in the organic medium inthe range of 8 wt. % to 11 wt. % of the total composition, for example.The thick film silver composition may be adjusted to a predetermined,screen-printable viscosity with the organic medium.

Fired Thick Film Compositions

In an embodiment, the organic medium may be removed during the dryingand firing of the semiconductor device. In an aspect, the glass frit,Ag, and additives may be sintered during firing to form an electrode.The fired electrode may include components, compositions, and the like,resulting from the firing and sintering process.

In an aspect of this embodiment, the semiconductor device may be a solarcell or a photodiode.

Method of Making a Semiconductor Device

An embodiment relates to methods of making a semiconductor device. In anembodiment, the semiconductor device may be used in a solar cell device.The semiconductor device may include a front-side electrode, wherein,prior to firing, the front-side (illuminated-side) electrode may includecomposition(s) described herein.

In an embodiment, the method of making a semiconductor device includesthe steps of: (a) providing a semiconductor substrate; (b) applying aninsulating film to the semiconductor substrate; (c) applying acomposition described herein to the insulating film; and (d) firing thedevice.

Exemplary semiconductor substrates useful in the methods and devicesdescribed herein are recognized by one of skill in the art, and include,but are not limited to: single-crystal silicon, multicrystallinesilicon, ribbon silicon, and the like. The semiconductor substrate maybe junction bearing. The semiconductor substrate may be doped withphosphorus and boron to form a p/n junction. Methods of dopingsemiconductor substrates are understood by one of skill in the art.

The semiconductor substrates may vary in size (length x width) andthickness, as recognized by one of skill in the art. In a non-limitingexample, the thickness of the semiconductor substrate may be 50 to 500microns; 100 to 300 microns; or 140 to 200 microns. In a non-limitingexample, the length and width of the semiconductor substrate may bothequally be 100 to 250 mm; 125 to 200 mm; or 125 to 156 mm.

Exemplary insulating films useful in the methods and devices describedherein are recognized by one of skill in the art, and include, but arenot limited to: silicon nitride, silicon oxide, titanium oxide,SiN_(x):H, hydrogenated amorphous silicon nitride, and siliconoxide/titanium oxide film. The insulating film may be formed by PECVD,CVD, and/or other techniques known to one of skill in the art. In anembodiment in which the insulating film is silicon nitride, the siliconnitride film may be formed by a plasma enhanced chemical vapordeposition (PECVD), thermal CVD process, or physical vapor deposition(PVD). In an embodiment in which the insulating film is silicon oxide,the silicon oxide film may be formed by thermal oxidation, thermal CVD,plasma CVD, or PVD. The insulating film (or layer) may also be termedthe anti-reflective coating (ARC).

Compositions described herein may be applied to the ARC-coatedsemiconductor substrate by a variety of methods known to one of skill inthe art, including, but not limited to, screen-printing, ink-jet,coextrusion, syringe dispense, direct writing, and aerosol ink jet. Inan embodiment, compositions may be applied to substrates using methodsand devices described in US patent application publication 2003/0100824,which is hereby incorporated herein by reference. The composition may beapplied in a pattern. The composition may be applied in a predeterminedshape and at a predetermined position. In an embodiment, the compositionmay be used to form both the conductive fingers and busbars of thefront-side electrode. In an embodiment, the width of the lines of theconductive fingers may be 10 to 200 microns; 40 to 150 microns; or 60 to100 microns. In an embodiment, the width of the lines of the conductivefingers may be 10 to 100 microns; 15 to 80 microns; or 20 to 75 microns.In an embodiment, the thickness of the lines of the conductive fingersmay be 5 to 50 microns; 10 to 35 microns; or 15 to 30 microns. In afurther embodiment, the composition may be used to form the conductive,Si contacting fingers.

The composition coated on the ARC-coated semiconductor substrate may bedried as recognized by one of skill in the art, for example, for 0.5 to10 minutes, and then fired. In an embodiment, volatile solvents andorganics may be removed during the drying process. Firing conditionswill be recognized by one of skill in the art. In exemplary,non-limiting, firing conditions the silicon wafer substrate is heated tomaximum temperature of between 600 and 900° C. for a duration of 1second to 2 minutes. In an embodiment, the maximum silicon wafertemperature reached during firing ranges from 650 to 800 C for aduration of 1 to 10 seconds. In a further embodiment, the electrodeformed from the conductive thick film composition(s) may be fired in anatmosphere composed of a mixed gas of oxygen and nitrogen. This firingprocess removes the organic medium and sinters the glass frit with theAg powder in the conductive thick film composition. In a furtherembodiment, the electrode formed from the conductive thick filmcomposition(s) may be fired above the organic medium removal temperaturein an inert atmosphere not containing oxygen. This firing processsinters or melts base metal conductive materials such as copper in thethick film composition.

In an embodiment, during firing, the fired electrode (preferably thefingers) may react with and penetrate the insulating film, formingelectrical contact with the silicon substrate.

In a further embodiment, prior to firing, other conductive and deviceenhancing materials are applied to the opposite type region of thesemiconductor device and cofired or sequentially fired with thecompositions described herein. The opposite type region of the device ison the opposite side of the device. The materials serve as electricalcontacts, passivating layers, and solderable tabbing areas.

In an embodiment, the opposite type region may be on the non-illuminated(back) side of the device. In an aspect of this embodiment, theback-side conductive material may contain aluminum. Exemplary back-sidealuminum-containing compositions and methods of applying are described,for example, in US 2006/0272700, which is hereby incorporated herein byreference.

In a further aspect, the solderable tabbing material may containaluminum and silver. Exemplary tabbing compositions containing aluminumand silver are described, for example in US 2006/0231803, which ishereby incorporated herein by reference.

In a further embodiment the materials applied to the opposite typeregion of the device are adjacent to the materials described herein dueto the p and n region being formed side by side. Such devices place allmetal contact materials on the non illuminated (back) side of the deviceto maximize incident light on the illuminated (front) side.

The semiconductor device may be manufactured by the following methodfrom a structural element composed of a junction-bearing semiconductorsubstrate and a silicon nitride insulating film formed on a main surfacethereof. The method of manufacture of a semiconductor device includesthe steps of applying (such as coating and printing) onto the insulatingfilm, in a predetermined shape and at a predetermined position, theconductive thick film composition having the ability to penetrate theinsulating film, then firing so that the conductive thick filmcomposition melts and passes through the insulating film, effectingelectrical contact with the silicon substrate. The electricallyconductive thick film composition is a thick-film paste composition, asdescribed herein, which is made of a silver powder, Zn-containingadditive, a glass or glass powder mixture having a softening point of300 to 600° C., dispersed in an organic vehicle and optionally,additional metal/metal oxide additive(s).

An embodiment of the invention relates to a semiconductor devicemanufactured from the methods described herein. Devices containing thecompositions described herein may contain zinc-silicates, as describedabove.

An embodiment of the invention relates to a semiconductor devicemanufactured from the method described above.

Additional substrates, devices, methods of manufacture, and the like,which may be utilized with the thick film compositions described hereinare described in US patent application publication numbers US2006/0231801, US 2006/0231804, and US 2006/0231800, which are herebyincorporated herein by reference in their entireties.

EXAMPLES

An organic medium was prepared by dissolving polymers in organic solventat about 100 C. Into the organic medium, other ingredients were added,including silver powder, glass frits, zinc oxide and other additives.The resulting mixture was dispersed by a three roll-milling process,known in thick film paste manufacturing industry. Compositions I, II,and III, shown in Table 1, were formed.

Pastes from the compositions I and II were filtered through a Roki40L-SHP-200XS filter capsule before print. Composition III was usedwithout filtration.

Pastes were evaluated at room temperature by a 3D-450 Smart Pump™printer that is made by nScrypt Inc, using re-useable ceramic pen tip ofID/OD 50/75 μm. Pump pressure was between 10 psi and 100 psi. Theprinting speed was between 200 mm per second and 300 mm per second. Thegap between pen tip and substrate surface is 150 μm.

Groups of ten four inches long lines were printed, dried in a box ovenat 150 C for 20 minutes, and fired in a belt furnace at 850 C peaktemperatures for 2 minutes.

TABLE I Summary of Silver Paste Compositions Composition CompositionIngredient Composition I II III Silver 81.05 Powder I Silver 81.05Powder II Silver 81.05 Powder III Glass Frit I 2.5 Glass Frit II 2.5Glass Frit III 2.5 Zinc Oxide 5.5 5.5 5.5 Organic 10.95 10.95 10.95Medium * based on wt % of total composition Silver powder I, a mixtureof spherical and flake shapes with size of D10 = 0.88, D50 = 4.60, D95 =10.73 microns. Silver powder II, a spherical shape powder, with size ofD10 = 1.0, D50 = 1.71, D95 = 4.41 microns and surface area of 0.44 m2/g.Silver powder III, a spherical shape powder, with size of D10 = 0.26,D50 = 0.45, D95 = 1.67 microns, with solid of 99.5%. Its surface area is1.0 m2/g. Glass frit I, SiO₂ 23.0%, Al₂O₃ 0.4%, PbO 58.8% and B₂O₃ 7.8%,based on wt % of glass composition, with a size of D10 = 0.36, D50 =0.61 and D95 = 1.44 microns. Glass frit II, SiO₂ 22.08%, Al₂O₃ 0.38%,PbO 46.68%, B₂O₃ 6.79%, TiO₂ 5.86% and PbF₂ 10.72%, based on wt % ofglass composition, with size of D10 = 0.42, D50 = 0.77 and D90 = 1.96microns. Glass frit III, SiO₂ 22.08%, Al₂O₃ 0.38%, PbO 46.68%, B₂O₃6.79%, TiO₂ 5.86% and PbF₂ 10.72%, based on wt % of glass composition,with a size of D10 = 0.34, D50 = 0.50 and D95 = 0.89 microns. Zincoxide, purchased from Aldrich Chemicals.

Example I

Composition I was able to go through the 50/75 micron pen tip under pumppressure less than 50 psi for less than a period of 5 minutes before thepen tip was clogged. The best resulting fired lines were 83 microns wideand 13 microns tall.

Example II

Composition I was able to go through the 75/125 micron pen tip underpump pressure less than 60 psi for less than a period of 30 minutesbefore the pen tip was clogged. The best resulting fired lines were 100microns wide and 12 microns tall.

Example III

Composition II was able to go through the 50/75 micron pen tip underpump pressure ranging from 10 psi to 100 psi for a period of at least 30minutes before printing was stopped. The best resulting fired lines were89 microns wide and 19 microns tall.

Example IV

A blend of composition II and composition III with a weight percentageratio of 95.5 to 4.5 was able to go through the 50/75 micron pen tipunder pump pressure ranging from 10 psi to 80 psi for a period of atleast 3 hours before printing was stopped. The best resulting firedlines were 67 microns wide and 25 microns tall.

Example V

Composition III could not be printed through a 50/75 micron pen tipunder a pump pressure larger than 30 psi. Under 30 psi, printing lastedfor less than 5 seconds before pen tip was clogged.

Example VI

Composition III could be printed through a 75/125 micron pen tip under apump pressure larger than 60 psi. Under 60 psi, printing lasted for lessthan 5 minutes before pen tip was clogged.

Example VII

A series of blends of composition II and III with ratios ranging from 90to 10 to 10 to 90 by weight was prepared and printed. Once thecomposition III was more than 30%, 50/75 micron pen tip was cloggedwithin 1 minute.

Example VIII

The efficiency of the above printed substrates are analyzed. Anexemplary efficiency test is provided below. It is predicted that theefficiency of the solar cell from Example IV will be greater than theefficiency of the solar cells from the other Examples.

Test Procedure-Efficiency

The solar cells built according to the method described herein aretested for conversion efficiency. An exemplary method of testingefficiency is provided below.

In an embodiment, the solar cells built according to the methoddescribed herein are placed in a commercial I-V tester for measuringefficiencies (ST-1000). The Xe Arc lamp in the I-V tester simulates thesunlight with a known intensity and irradiated the front surface of thecell.

The tester uses a multi-point contact method to measure current (I) andvoltage (V) at approximately 400 load resistance settings to determinethe cell's I-V curve. Both fill factor (FF) and efficiency (Eff) arecalculated from the I-V curve.

1. A composition comprising: (a) one or more conductive materials; (b)one or more inorganic binders; and (c) organic vehicle, wherein 1 to 15%of the inorganic components are submicron particles.
 2. The compositionof claim 1, wherein 85 to 99% of the inorganic components have a d50 of1.5 to 10 microns.
 3. The composition of claim 1, wherein the one ormore conductive materials comprise silver.
 4. The composition of claim3, wherein the submicron particles comprise silver.
 5. The compositionof claim 1, wherein the submicron particles have a d50 of 0.1 to 1microns.
 6. The composition of claim 1, wherein the submicron particleshave a d50 of 0.1 to 0.6 microns.
 7. The composition of claim 1, whereinthe inorganic components have a bimodal size distribution.
 8. Thecomposition of claim 1 further comprising one or more additives.
 9. Thecomposition of claim 8, wherein the one or more additives comprisecomponents selected from the group consisting of: (a) a metal whereinsaid metal is selected from Zn, Pb, Bi, Gd, Ce, Zr, Ti, Mn, Sn, Ru, Co,Fe, Cu, and Cr; (b) a metal oxide of one or more of the metals selectedfrom Zn, Pb, Bi, Gd, Ce, Zr, Ti, Mn, Sn, Ru, Co, Fe, Cu and Cr; (c) anycompounds that can generate the metal oxides of (b) upon firing; and (d)mixtures thereof.
 10. The composition of claim 9, wherein the one ormore inorganic additives comprises ZnO.
 11. The composition of claim 4,wherein the submicron particles further comprise ZnO and an inorganicbinder.
 12. The composition of claim 1, wherein the one or moreinorganic binders comprise glass frit.
 13. The composition of claim 1,wherein the inorganic components are 70 to 95 wt % of the totalcomposition.